package org.scribe.services;

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import org.apache.commons.codec.binary.Base64;
import org.scribe.exceptions.OAuthSignatureException;
import org.scribe.utils.OAuthEncoder;
import org.scribe.utils.Preconditions;

/**
 * HMAC-SHA1 implementation of {@SignatureService}
 * <p/>
 * @author Pablo Fernandez
 * <p/>
 */
public class HMACSha1SignatureService implements SignatureService {

  private static final String EMPTY_STRING = "";
  private static final String CARRIAGE_RETURN = "\r\n";
  private static final String UTF8 = "UTF-8";
  private static final String HMAC_SHA1 = "HmacSHA1";
  private static final String METHOD = "HMAC-SHA1";

  /**
   * {@inheritDoc}
   */
  public String getSignature(String baseString, String apiSecret, String tokenSecret) {
    try {
      Preconditions.checkEmptyString(baseString, "Base string cant be null or empty string");
      Preconditions.checkEmptyString(apiSecret, "Api secret cant be null or empty string");
      return doSign(baseString, OAuthEncoder.encode(apiSecret) + '&' + OAuthEncoder.encode(tokenSecret));
    } catch (Exception e) {
      throw new OAuthSignatureException(baseString, e);
    }
  }

  private String doSign(String toSign, String keyString) throws Exception {
    SecretKeySpec key = new SecretKeySpec((keyString).getBytes(UTF8), HMAC_SHA1);
    Mac mac = Mac.getInstance(HMAC_SHA1);
    mac.init(key);
    byte[] bytes = mac.doFinal(toSign.getBytes(UTF8));
    return new String(Base64.encodeBase64(bytes)).replace(CARRIAGE_RETURN, EMPTY_STRING);
  }

  /**
   * {@inheritDoc}
   */
  public String getSignatureMethod() {
    return METHOD;
  }
}
